A tire bead is that part of a tire which has a function of locating and fixing textile or steel cords of a carcass ply, determining the internal periphery of the tire, and anchoring the tire onto a wheel rim. The tire bead is essentially an annular, tensile member or inextensible hoop. Every tire has at least two tire beads which are located within the rubber or elastomeric matrix that makes up the radially inner-most circumference on each side of the tire. There are three primary conventional categories of tire beads, they are strap beads, single wire beads and cable beads.
Strap Beads
An example of a strap bead is disclosed in European Patent Application No. 655,354 wherein a bead core is constructed by winding a strip of wire-rubber matrix made of a row of several wires buried in rubber, as shown in FIG. 1 herein. The rubber keeps the bead together and prevents fretting of the wire into adjacent components of the tire. A strap bead is easy and economical to manufacture. There are, however, some drawbacks to strap beads. First, the inner and outer ends of the strap overlap and are spliced, wrapped or stapled together. The weakest region of this type of bead is at the overlap of the strap ends. Also, in the manufacture of a pneumatic tire incorporating strap beads, the rows and lines of the wire-rubber matrix tend to fall in disorder during the tire building and curing steps and it can adversely affect the uniformity of the tire.
Single Wire Beads
The single wire bead is constructed by wrapping a single strand of rubber coated bead wire into a bundle or hoop of a desired cross sectional shape. The cross-sectional shape can be defined as, but not limited to, hexagonal, triangular, square or pentagonal. The number of turns that the bead wire is wound depends upon the strength and/or cross-sectional area of the tire bead desired. For example, as shown in FIG. 2 herein, a single rubber-coated bead wire is wrapped nineteen (19) times into a cylindrical bundle or hoop that forms an hexagonal shaped bead. Note that the wraps begin on the inner row, left-hand corner, move to the right, then up and back toward the left, and then up and to the right. The free ends of the bead wire can be secured by a number of techniques including pushing them into the bundle, and/or stapling or taping them to the bundle. A single wire bead is the strongest of the conventional prior art beads described herein. The deficiencies of a single wire bead are a) since the single wire bead is wound of a single wire, the production time is often longer and therefore the single wire beads are generally more expensive to manufacture; and b) also, the free ends of the wound bead wire have a spring-back nature and sometimes come loose from the bundle causing tire misalignments, a protuberance from the tire, and/or some tire imbalance.
Cable Beads
A conventional cable bead typically consists of a core hoop formed of a single wire having its ends typically welded together. Then a cable, consisting of one or more filaments of wire, is helically wound around the core hoop. Next, one free end of each filament is connected to the opposite free end, typically by inserting the free ends into a ferrule and crimping the ferrule. The deficiencies in this cable bead construction generally include a) the core tending to break at the weld; b) the cable filament wire tending to break at the ferrule causing the free ends of the wound cable wire which have a spring-back nature to sometimes come loose from the bundle causing tire misalignments, a protuberance from the tire, and/or some tire imbalance. An example of this type of cable bead construction is set forth in G.B. 189,429 and U.S. Pat. No. 1,491,626.
Another prior art cable bead design, as disclosed in U.S. Pat. No. 1,715,302, can be constructed of a core hoop formed of a group of wires twisted together. The ends of the wires forming the core hoop can be secured to each other, typically by welding them together. Then, a cable consisting of one or more filaments of wire is helically wound around the core hoop. The ends of each filament of the cable are connected to each other, typically by inserting them into a ferrule and crimping the ferrule to secure the ends therein. When two or more cable layers are wound about the core, they are preferably wound in opposite directions to each other. The deficiencies in this cable bead construction include: a) the added time and expensive due to the core being formed of a group of twisted wires; and b) the cable filament(s) tending to break at the ferrule causing the free ends of the wound cable wire which have a spring-back nature to sometimes come loose from the bundle causing tire misalignments, a protuberance from the tire, and/or some tire imbalance.
Still another prior art cable bead design, as disclosed in U.S. Pat. No. 1,437,013 ('013), can be constructed of a core that “consists of three convolutions of wire laid side by side in such a relation as to form a triangular cross section the arrangement being such that two of the convolutions lie side by side and the third lies on the outer side of these two convolutions directly over their adjacent sides. The core so formed is of triangular cross section with one of its sides toward the inner side of the core and the inner side of the completed grommet and the apex of the triangle toward the outer side of the grommet” (page 1, lines 39-51). The three convolutions . . . are preferably formed from a continuous piece of wire . . . ” (page 1, lines 100-102). The ends of the wire forming the core can be secured to each other, “as by welding them together” (page 1, lines 108-109). Then, “a plurality of convolutions of spirals are wound upon the core so formed with the spirals of several convolutions lying side by side and forming a complete layer or casing.” (page 1, lines 52-56). “The end of the wire forming the surrounding casing may be secured in position in any suitable manner” (page 2, lines 12-14). When the surrounding casing of spirally formed wire has been completed, the grommet is substantially in the form indicated in FIG. 2 of the '013 patent, the spirals of the casing being arranged approximately in a circle about the triangular core.
The grommet so formed as an intermediate product of construction is then subjected to heavy pressure to expand it to the desired size. While so expanding the grommet, the casing of spirals assumes a configuration more or less approximating the cross-sectional shape of the core so that the completed grommet is substantially triangular in cross-section. The relation of the core wires and the wires of the spiral casing after the grommet has been so expanded is indicated in FIG. 3.
During the intermediate stage of construction, when the grommet is in the form as shown in FIG. 2, the spirals of the casing are arranged approximately in a circle about the triangular core. However, after the grommet has been formed into an intermediate article of manufacture, as previously discussed, the grommet is preferably stretched to enlarge it to the precise diameter desired for the completed grommet. The disclosure of expanding the grommet by heavy pressure from the size shown in FIG. 2 of the '013 patent up to the desired size as shown in FIG. 3 of that patent is not readily understandable. While the multiple convolutions of single wound wire forming the triangular core of the bead must have enough flexibility that the bead portions of the tire can be mounted on a rim, they must concurrently be stiff and strong enough that tire remains mounted on the rim during the stresses generated under normal operating conditions. Moreover, it seems likely that the wound wire would be stretched beyond its elastic limit and therefore be unable to return to its design shape. Therefore, it seems unlikely that the core would be unable to stretch from the diameter shown in FIG. 2 to the diameter shown in FIG. 3 while retaining its functional requirements due to the strength requirements of the grommet. This ability to stretch is even less likely in the bead design where the ends of the wire forming the core are joined together, as by welding. With this design, the core would have the tendency to break at the weld.
It is further not understood from the disclosure of the '013 patent how the surrounding casing or casings of spirally wound wires would shift from their initial circular configuration (shown in FIG. 2 of the '013 patent) to a triangular shape (shown in FIG. 3 of the '013 patent) corresponding to that of the enclosed triangular shaped core (a triangular shape with one of its sides toward the center of the grommet and its apex directed outwardly of the grommet). The spirally wound wire(s) are wound about the core so as to cross all of the core wires as they spiral along the length of the core from one end to the other. When a device (not shown) is inserted into the grommet to stretch it outwardly, the device would be forced to press the casing wires at spaced locations against the core wires which would in turn cause the casing wires to resist being stretched. And even if they could stretch, it is not understandable how they could stretch to a triangular shape since they would not be free to stretch evenly.
Another apparent structural contradiction in the '013 patent is that, similar to the triangular core, the convolutions of wound wire forming the casing of the bead must have enough flexibility that the bead portions of the tire can be mounted on a rim. They must concurrently be stiff and strong enough that tire remains mounted on the rim during the stresses generated under normal operating conditions. Moreover, it seems likely that the wound wire of the casing would be stretched beyond its elastic limit and therefore be unable to return to its design shape. Therefore, it seems unlikely that the casing would be able to stretch from the diameter shown in FIG. 2 of the '013 patent to the diameter shown in FIG. 3 of that patent while retaining its functional requirements due to the strength and stiffness requirements of the grommet needed for the bead to function properly in a tire.
Regarding the functionality of conventional cable beads, it is believed that the core of the prior art cable beads were primarily used as a mandrel to wrap the cabling around. When a prior art cable bead of the types described herein before is incorporated into a green tire carcass, the cable does not stick or attach itself to the green rubber of the ply when the ply ends are wrapped around the cable beads and pressed against the main body of the ply on the first stage tire building drum. Then, when the tire carcass is shaped into a toroidal cross section on the first stage tire building drum, the material around the cable tends to slip about the cable bead so that uniformity problems possibly caused by the bead being twisted (such as single wire or strap beads) are reduced. Then, after the tire is cured, the core is no longer needed and the strength of the bead is primarily derived from the cabling. The cabling of the prior art cable beads, while providing the primary strength of the bead, is also generally flexible. The flexibility of the prior art cable beads is advantageous in that the tire is easier to mount on a wheel. However, the flexibility has an important disadvantage. That is, the flexible nature of the prior art cable beads also causes them to more easily unseat from a wheel, especially during adverse load conditions such as with deflated or under-pressurized tires.
Another cable bead design as disclosed in Japanese Laid-Open Patent Application 55-1201 entitled BEAD WIRE discloses for example, a “composite bead wire, as shown in FIG. 4, a hard steel solid wire W14 coated with rubber coating R2 was sequentially wound in parallel so that they were in close contact with one another and stacked and wound, resulting in a formed bead wire main body with a hexagonal cross-section. With this as the cord ring, its peripheral surface was spirally wound with a hard steel wire W15 and the entire peripheral surface of the core ring was surrounded, resulting in a bead wire characterized by a circular cross-section.” (See P. 15 of translation). In another embodiment, as shown in FIG. 5 of the 55-1201 Application, “a rubber coating R3a is applied to a single hard steel wire W16 using a rubber extruder, and that hard steel wire W16 is wound three times in parallel on a winder former to form a first layer.” Using additional winders can be layered to form “a bead wire main body 1 whose cross-section shape is hexagonal.”
“Next, a rubber coating R4 is applied to a hard steel wire W17 using a rubber extruder to make a rubber coated wire 2. Using the aforesaid bead wire main body 1 as a core ring, the rubber coated wire 2 is spirally wound . . . on its peripheral surface, and the entire peripheral surface of the bead wire main body 1 . . . ” (See pages 15 and 16 of the translation). This patent application has a limitation in that the rubber coated wire forming the bead wire main body is in contact with the rubber coating the rubber coated wire disposed about the bead wire main body so that the surrounding wire and main bead wire have a tendency not to move with respect to each other during the manufacture of the tire prior to the molding process.
In a Japanese Laid-Open Patent Application 51-50106, there is disclosed a composite bead wire wherein a ring body B3 formed of a hard steel solid wire W11 with a rubber coating R2 has a hard steel wire W12 spirally wound about the peripheral surface at a suitable pitch. A rubber coating or a fabric coating can be applied to fill the gap between the ring body's B3 hexagonal cross-section and the circular cross-section of the peripheral spiral winding using the hard steel wire W12.” This patent application can be distinguished from the present invention in that the application of a rubber coating or fabric coating between the ring body and the spiral winding would also prevent the movement of the spiral winding with respect to the ring body during the manufacture of the ring.
Thus, despite the existence of several types of beads in the prior art, there still exists a need for an improved tire bead construction that can reduce or eliminate the above-described difficulties.